Why does scaling my UVs have any visible effect in the 3D View?
The only shading modes that allow an accurate view of your shaders are the material view and rendered view. Solid view using texture color display might not always show textures as they are, especially their mapping.
Also, what you see depends on your material's nodes setup.
Finally, I'd advise avoiding scaling UVs, it's usually a better idea to keep them correctly done in their UV space and use mapping nodes in your materials to dissort them.